Winter irrigation termination: Water can be conserved in alfalfa
production by not irrigating during the winter. In a test conducted on
the Yuma-mesa, alfalfa irrigations were terminated from November through
February with only a slight impact on yield. Winter rainfall is often
sufficient to maintain some growth without supplemental irrigation. The
advantage of winter compared to summer irrigation termination is that
haymaking is difficult during the winter and permanent damage is not as
likely with winter termination.

Insect Management: Pea aphid, a pest of alfalfa during the spring
months, can be distinguished from blue alfalfa aphid by lighter antennae
with dark bands at each joint. Blue alfalfa aphids have uniformly dark
antennae. Pea aphids first appear in December or January but are usually
less abundant than blue alfalfa aphid until later in the spring, but pea
aphid may persist into early summer as they are more heat tolerant. They
are found over most of the plant with heavy infestations and can deposit
large quantities of honeydew which can foul harvesting equipment and supports
the growth of sooty molds lowering hay quality. Regrowth may be stunted
following cuttings with moderate to heavy aphid populations. Several species
of predacious bugs and parasitic wasps attack these aphids. Sample alfalfa
fields by taking 5 to 6 stem samples in at least 5 locations per field
weekly when aphids appear, then every 2 to 3 days as numbers approach
the treatment threshold of 40 to 50 aphids per stem for plants under 10
inches, 70 to 80 per stem for plants 10 to 20 inches tall and more than
100 aphids per stem for plants over 20 inches tall.

Weed Control: It is better to be a month early than a day late
with preemergent herbicides. It is best to shoot for mid-January to February
1 in alfalfa. It needs to get very cold to kill weeds like sprangletop
and sandbur. Preemergent herbicides will not kill weeds that overwinter.

Issued in furtherance of Cooperative Extension work, acts
of May 8 and June 30, 1914, in cooperation with the U.S. Department of Agriculture,
James A. Christenson, Director Cooperative Extension, College of Agriculture
and Life Sciences, The University of Arizona.

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